Injury to the endothelial cells that line the lumen of the artery will alter the permeability of the cells. This may allow cholesterol and other lipids from the blood lipoproteins to enter the arterial cells and arterial walls. This may initiate the process of atherosclerosis. Vitamin D is one of the many biological compounds that can injure the endothelial cells. The areas having changes in vascular permeability can be identified by uptake of dyes. Diets that induce atherosclerosis will be fed to rats and the concentration of blood cholesterol, triglycerides and the lipoprotein patterns will be determined. High levels of dietary vitamin D have induced atherosclerotic lesions without significantly altering the sepum lipids. The mechanism of these lesions and the exact type of atherosclerotic plaques are being investigated. Organ cultures of aortas and subcellular fractions thereof will be used to study the in vitro uptake of calcium and specific blood lipids. Proteins from the serum of rats having atherosclerotic plaques may influence the uptake by the aorta or organelles thereof and may influence the progression and development of atherosclerosis. The regression of plaques, or at least the inhibition of the rate of progression of plaques will be studied in a similar manner, i.e., comparing the severity of the lesion with the in vitro uptake of specific compounds.